The term "electrical machining" is used herein to describe electrochemical machining (ECM) and electrical-discharge machining (EDM) both of which apply electrical energy between an electrode and a workpiece, usually across a coolant-filled gap to remove material from the workpiece in a predetermined pattern, generally controlled by the configuration of the electrode. In electrical-discharge machining, the electrical energy applied across the electrode/workpiece system is a capacitive discharge and/or a switched high-energy pulse which breaks down the dielectric fluid in the gap and produces a spark-type discharge bridging the electrode and workpiece, the high kinetic energy of the discharge effecting mechanical removal of the material, localized melting and some degree of vaporization of the workpiece surface. In electrochemical machining, however, the material is removed in accordance with Faraday's law as a result of the application of a substantially unidirectional electric current, or the use of an electrical current having a unidirectional component, to solubilize the workpiece material in the electrolyte forming the coolant.
Electrical-discharge machining, electrochemical machining and high-energy-rate-forming using impulsive discharges as the energy source, have been described in my prior U.S. Pat. Nos. 3,333,081 of July 25, 1967; 3,378,473 of Apr. 16, 1968; 3,232,085 of Feb. 1, 1966; 3,616,343 of Oct. 26, 1971; 3,512,384 of May 19, 1970; 3,417,006 of Dec. 15, 1968; 3,475,312 of Oct. 28, 1969; 3,361,268 of Aug. 12, 1969, and my pending application Ser. Nos. 157,575 of June 28, 1971, now U.S. Pat. No. 3,814,392; 125,192 of Mar. 17, 1971, now U.S. Pat. No. 3,727,489 and 19,364 of Mar. 13, 1970, now U.S. Pat. No. 3,686,461.
These patents, applications, and the references therein cited, disclose various methods in which bodies may be shaped or contoured to the desired configuration. Difficulties have, however, been encountered in the finishing of workpieces using these techniques and even without electrical machining processes the actual finish shaping of highly contoured bodies is difficult. Furthermore, the electrical systems require dies and electrodes of high accuracy and it is often difficult to make electrodes for EDM and ECM purposes in materials such as graphite, where the configuration or topography of the body is complex. Even the finishing of graphite bodies is difficult, when the body is intended for use in an EDM or ECM system.
In recent times, die-using technology is important is many fields of industry where it has been found to replace conventional cutting technology to achieve an improved productivity of articles. Thus, the need for dies in number and kind goes on expanding and recent tendencies show increased demand for larger and larger and/or more or more intricated dies. Die-making, however, represents generally a low quantity output and versatile requirement manufacture and in accordance with currently available methods is a relatively time-consuming and expensive job. Thus, a die shaped with a conventional miller must be finished to eliminate tool marks and pick-feed marks formed on the surface and to meet a strictly due dimensional accuracy and this has been done by hands requiring a relatively high level of skill and a great amount of time. A cost involved in such laborious inspection/finishing work constituted a major part of the total cost involved in the production of a die and even a significant part of the entire cost for articles requiring die and designed to be made therefrom.